The present invention relates to apparatus for transferring objects, such as ferromagnetic workpieces, and more particularly to improvements in apparatus which employ one or more lifting electromagnets. Still more particularly, the invention relates to improvements in lifting electromagnets which can be used to supply workpieces to or remove workpieces from the treating or processing stations of machine tools or the like and which are equipped with or embody one or more sensors serving to generate signals when they move sufficiently close to or when they are approached by one or more ferromagnetic or other objects which are capable of changing the characteristics of the electromagnetic field.
German Offenlegungsschrift No. 25 54 046 discloses a lifting electromagnet wherein the exciting coil of the electromagnet simultaneously performs the function of an induction coil. A voltage is induced in the coil in response to changes of the magnetic field, and such voltage constitutes a signal which can be used to control the operation of the apparatus embodying the electromagnet. The apparatus which is disclosed in this German publication is capable of ascertaining whether or not a ferromagnetic object has entered the magnetic field; however, the coil is incapable of furnishing an indication as to the exact position of the object with reference to the electromagnet and/or vice versa.